The pre-existing Fermi level alignment between ZnO and CuSCN semiconductors gives rise to the two key elements needed for a self-powered, binary-response UV-sensor: photovoltaic behavior and low turn-on bias. Nanosecond response times, self-powered performance, and long-term stability, coupled with scalable, inexpensive fabrication on the nanoscale, offer currently unmatched progression towards self-sufficient nanoscale systems.